The polymerization of hemoglobin S molecules into fibers and alignment of these fibers to form a crystalline phase (gelation) is responsible for the deformation (sickling) of the red blood cell in sickle cell anemia. The interpretation of both kinetic and equilibrium experiments on the gelation of hemoglobin S requires thermodynamic information. BIBLIOGRAPHIC REFERENCES: Ross, P.D., Hofrichter, J. and Eaton, W.A.: Thermodynamics of Gelation of Sickle Cell Deoxyhemoglobin. J. Mol. Biol., in the press, 1977. Ross, P.D. and Minton, A.P.: analysis of Non-Ideal Behavior in Concentrated Hemoglobin Solutions. J. Mol. Biol., in the press, 1977.